#include <bits/stdc++.h>

#define in read()
#define fi first
#define se second
#define pb push_back
#define rep(i, x, y) for(int i = (x); i <= (y); i++) 
#define per(i, x, y) for(int i = (x); i >= (y); i--)

using namespace std;

using ll = long long;
using db = double;
using pii = pair < int , int >;
using vec = vector < int >;
using veg = vector < pii >;

int read() {
	int x = 0; bool f = 0; char ch = getchar(); while(!isdigit(ch)) f |= ch == '-', ch = getchar(); 
	while(isdigit(ch)) x = x * 10 + (ch ^ 48), ch = getchar(); return f ? -x : x;
}

const int N = 1e5 + 10;
const int mod = 1e9 + 7;

int n, m;

int main() {
#ifndef ONLINE_JUDGE
	freopen("1.in", "r", stdin);
#endif
	cin >> n >> m;
	if(abs(n - m) > 1) cout << 0 << endl;
	else if(n == m) {
		ll res = 1; rep(i, 1, n) res = res * i % mod;
		cout << res * res % mod * 2 % mod<< endl;
	} else {
		ll res = 1; rep(i, 1, n) res = res * i % mod; rep(i, 1, m) res = res * i % mod;
		cout << res << endl;
	}
	return 0;
}
